Due to the world's depleting reserves of fossil fuels such as oil, there exists a need for alternative fuel vehicles (AFV's). The Energy Policy Act (EPACT) signed by President Bush in 1992 requires that states and the federal government take steps to reduce energy use and to shift to other sources of energy, including the addition of alternative fuel vehicles (AFV's) to federal and state fleets. Individual states such as California and New York have instituted goals of near-zero emission standards for percentages of new vehicles sold within those states in the near future. Thus, the need exists for alternative fuels.
Natural gas has long been considered an excellent alternative fuel since it is considered much cleaner than other fossil fuels such as oil, and its reserves are much larger than crude oil. Natural gas which is primarily composed of methane and combinations of Carbon Dioxide, Nitrogen, Ethane, Propane, Iso-Butane, N-Butane, Iso Pentune, N-Pentane, and Hexanes Plus, is a renewable energy source since anaerobic bacterial eventually will convert all plants into methane type gas. Natural gas has an extremely high octane number, approximately 130, thus allowing higher compression ratios and broad flammability limits.
A problem with using natural gas is reduced power output when compared to gasoline, due mostly to the loss in volumetric efficiency with gaseous fuels, as well as the lack of the infrastructure for fueling natural gas vehicles. Another problem area is the emissions produced by these natural gas vehicles. Although, the emissions are potentially less than that of gasoline vehicles, these vehicles generally require some types of emissions controls such as exhaust gas recirculation (EGR), positive crankcase ventilation (PCV), and/or unique three-way catalyst. A still another problem with using natural gas vehicles is the slow flame speed which requires that the fuel be ignited substantially before top dead center (BTDC). In general, most internal combustion engines running on gasoline operate with a spark advance of approximately 35 degrees BTDC where as the same engine operating on natural gas will require an approximate advance of 50 degrees BTDC. The slower burn rate of the fuel results in reduced thermal efficiency and poor burn characteristics.
Proposed alternative fuels utilizing hydrogen and fossil fuels have also been used with resulting problems. In an article entitled Houseman et al., "A Two-Charge Engine Concept: Hydrogen Enrichment" SAE Paper #741169 (1974), research was conducted at the Jet Propulsion Laboratory. The researchers ran a V-8 internal combustion engine on a mixture of gasoline and hydrogen. The addition of hydrogen allowed the engine to be operated much leaner than was possible on gasoline alone. The result of this research was that NO.sub.x emissions were reduced below the 1977 EPA standard of 0.4 gm per mile. The article states that "At an equivalence ratio of 0.53, very low NO.sub.x and CO were produced and engine thermal efficiency was substantially increased over stock gasoline configurations. The article mentions that in order to "operate a vehicle on fuel mixtures of gasoline and hydrogen, an onboard source of hydrogen is required. Onboard storage of hydrogen, either as a compressed gas, as a liquid at cryogenic temperature, or as a hydride is not a practical solution today. Direct generation of hydrogen from gasoline in an onboard reactor was selected as the best solution to the problem." The main problem with this device was that the reactor described has not been adopted due to the complexity of the device.
The articles by MacDonald, J. S., entitled "Evaluation of the Hydrogen Supplemented Fuel Concept with an Experimental Multicylinder Engine" Automotive Engineering Congress and Exposition, SAE Paper #760101 (1976), and by Parks, F. B., entitled "A Single-Cylinder Engine Study of Hydrogen-Rich Fuels" Automotive Engineering Congress and Exposition, SAE Paper #760099 (1976) were by authors from General Motors that also investigated the use of hydrogen-enriched gasoline. Reflecting on Houseman et al.'s work, MacDonald states that, "while this approach (hydrogen reactor) as been shown to be feasible, it does have its limitations. A problem is the maximum theoretical yield of hydrogen per pound of fuel is about 14% by weight. Another problem is the hydrogen generator is at best only 80% efficient, so that any gasoline going to the generator represents an efficiency loss, which is a loss in fuel economy. For these reasons it is desirable to keep the quantity of hydrogen required for acceptable engine operation to a minimum. This article goes on to report that when 14.4% of the fuel mass was hydrogen the engine operated satisfactorily with an equivalence ratio of 0.52 and the NO.sub.x levels had dropped below the EPA mandated level of 0.4 gm per mile.
Several U.S. patents have incorporated similar concepts. For example, U.S. Pat. No. 4,376,097 to Emelock describes a hydrogen generator for motor vehicles. U.S. Pat. No. 4,508,064 to Watanabe describes a customized engine for burning hydrogen gas. U.S. Pat. No. 5,176,809 to Simuni describes a technique of producing and recycling hydrogen from exhaust gases.
Some research has been conducted for corabining hydrogen and natural gas as a fuel mixture. Articles by Nagalingam et al. entitled: "Performance Study Using Natural Gas, Hydrogen-Supplemented Natural Gas and Hydrogen in AVL Research Engine", International Journal of Hydrogen Energy, Vol 8, No. 9, pp. 715-720, 1983; Fulton et al. entitled: "Hydrogen for Reducing Emissions from Alternative Fuel Vehicles" 1993 SAE Future Transportation Conference, SAE Paper from Alternative Fuel Vehicles" 1993 SAE Future Transportation Conference, SAE Paper #931813, (1993) and an article by Yusuf entitled: "In Cylinder Flame Front Growth Rate Measurement of Methane and Hydrogen Enriched Methane Fuel in a Spark Ignited Internal Combustion Engine, Unpublished Masters Theseis, University of Miami (1990) each disclosed such combinations of a fuel mixture. However, the mixtures were generally limited to 20% hydrogen and the rest generally methane.
U.S. Pat. No. 5,139,002 to Lynch et al., states that hydrogen enriched mixtures should only contain mixtures of up to levels of between 10 and 20%." See column 9, lines 49-60, and column 16, lines 14-21. At column 9, lines 37-60, Lynch et al. states that "Relatively few tests were necessary to rule out the 25% and 30% mixtures (of hydrogen). . . "
Despite its clean burning characteristics, the utilization of hydrogen has had many problems as an alternative fuel. Primarily, the use of hydrogen in vehicles has been limited by the size, weight, complexity and cost of hydrogen storage options as well as the cost of hydrogen.
The controlling of air/fuel ratios and engine power has been limited in past applications. Generally, a spark ignition (SI) engine's power is controlled through a process called throttling. Throttling controls the volume of air that enters a combustion engine. The throttle system is formed from one or more throttle blades which are placed in the air inlet stream. During a "closed throttle" position also referred to as IDLE, the throttle blade closes off the air inlet and the only air entering the engine is leakage passing through the blades. Alternatively, the only air entering the engine can be air passing through a small hole in the throttle blade to provide a minimum amount of air to the engine. When the throttle is wide open, the throttle blade is parallel to the air stream and it presents a minimal air restriction to the incoming air. Most often the throttle blade is between full open and fully closed thus presenting a controlled restriction to the air passage.
Fuel in a spark ignition (SI) engine is generally introduced into the inlet air stream to provide the air fuel mixture for combustion. Various methods have been used for introducing the fuel into the air. For example, the carbureted SI engine is the most common method for automotive applications. Here, the carburetor controls the amount of fuel injected into the air stream by the fuel orifice size and the pressure drop across a venturi. To increase the amount of fuel to be injected given a constant pressure drop, the size of the jet was increased. With a fixed jet size, the amount of fuel entering the air stream remained virtually proportional to the pressure drop across the ventur. Thus, the pressure drop across the ventur was a function of throttle position.
An alternative known method of introducing fuel into the air stream is a fuel injector. The fuel injector can be located in a common plenum which feeds all of the cylinders on a multicylinder engine. At this location, the engine is said to be "throttle body injected." The injectors can alternatively be located in the intake runners feeding the individual runners. This type of injection is referred to as "port injection."
In both the throttle body and the port injection systems a sensor is needed to measure the amount of air entering the engine in order to control the injectors and produce a constant air/fuel ratio over the full range of throttle openings. Generally the output signal from a pressure sensor or a flow sensor is fed to a computer which uses the analog of the air flow from the sensor to control the length of time the injector is to be open and thus control the air/fuel ratio. Additional sensors have also been included to measure throttle position and exhaust oxygen content. Output from these sensors also can control the air/fuel ratio.
Power output of an engine has also been controlled strictly by the amount of fuel introduced into the combustion chamber just prior to ignition. In compression ignition (CI) engines also referred to as "Diesel Engines", the CI engine does not usually have a throttle. Air entering the engine is only restricted by the intake manifold design. Fuel is injected directly into the cylinder of the CI engine just prior to ignition. The ignition is caused by the high heat generated during the compression stroke.
Examples of the above prior art can be found in U.S. Patents: U.S. Pat. No. 3,982,878 to Yamane et al.; U.S. Pat. No. 4,184,461 to Leung; U.S. Pat. No. 4,213,435 to Simko; U.S. Pat. No. 4,244,023 to Johnson; U.S. Pat. No. 4,406,261 to Ikeura U.S. Pat. No. 4,471,738 to Smojver; U.S. Pat. No. 4,512,304 to Snyder; and U.S. Pat. No. 4,730,590 to Sogawa.
Operating an engine at lean burn was attempted by U.S. Pat. No. 4,499,872 to Ward et al. However, the Ward system is restricted to an adiabatic engine design and requires elaborate structural components and connections such as a microwave generator in order to operate.